Most catheters used in interventional medicine are sterile, single-use products, which are disposed after the procedure. Catheters are inserted intraluminally, including intravascular and non-intravascular placement. Catheters can also be inserted interstitially. Many catheters used for diagnosis or treatment, are designed to be used over a range of axial insertion depths. Usually the distal end of the catheter contains a diagnostic or therapeutic element that needs to be placed in the desired target area. Oftentimes, the target area in the body is longer than the diagnostic or therapeutic element, and so the catheter needs to be moved along the target area, so that the entire area can be either diagnosed or treated. For example, in intravascular ultrasound (IVUS), a catheter with one or more ultrasonic transducers at its tip is gradually pulled back along the length of a blood vessel or vascular structure in order to produce an ultrasonic image of the vessel and its disease.
In some applications catheters are pulled or pushed by means of pullback devices. These devices are usually attached to the proximal end of the catheter that extends out of the patient. The devices have a motor that serves to move the catheter at a steady rate in the desired longitudinal direction. This in turn moves the distal element of the catheter through the desired range in the target area. Because the pullback devices have motors and other relatively expensive mechanical and electrical components, they are often constructed and supplied as non-sterile, reusable devices. These devices usually need to be close to the patient, so it is often desirable to place them on the sterile field, for example, on top of the patient's legs or between the patient's legs. In order to place these devices in the sterile field, they are typically covered with a low cost, sterile clear bag, which allows manipulation of the buttons and visualization of the controls. Polyethylene is a common material used, due to its lost cost, transparency and sufficient strength at low wall thickness.
In the past, some IVUS pullback devices have consisted of two main parts, a motor drive and a sled. These parts are separable from each other, and are attached together prior to use. For example, in Cardiovascular Imaging Systems 510(k) # K933517, dated Jul. 16, 1993, the motor drive has a separate motor for rotating a drive shaft containing an ultrasonic transducer at the tip. The sled has its own longitudinal drive motor. In this device, known commercially as the Boston Scientific ClearView pullback device, two sterile bags are used, one to cover the motor drive and one to cover the sled. After attaching the two covered parts to each other, the entire assembly can be placed on the sterile field. In use, the bag that covers the sled is forced to bunch up, due the translation between the carriage of the sled and the base of the sled. For this reason, the user must manually create slack in the sled bag prior to fully attaching the catheter and beginning a pullback.
At least two different alternative configurations have been attempted for a two piece motor drive and sled pullback device, which only requires one sterile bag. Placing one bag is more desirable than two bags, because it requires less time and complexity in the set up. In the device presented in U.S. Pat. No. 6,309,358, the sterile bag has a locking interface. The bag is placed over the pullback device and the interface is locked to the pullback device. The catheter is then locked into the interface. Though there is only one bag covering the pullback device, the bag must still be bunched up by the user prior to the procedure. In addition, the catheter is not directly attached to the pullback device, so there is an additional attachment step. The device presented in U.S. Pat. No. 6,398,755, consists of a reusable motor drive and a disposable sterile sled. A single bag is placed over the motor drive and the sterile sled is attached to the motor drive by piercing the bag at the interface point. Because the carriage of the sled and the base of the sled are sterile, and do not need to be covered with a bag, there is no bunching up for the user to be concerned with. However, the user must now purchase not only the sterile bag but also a sterile sled for each procedure, increasing the cost per patient. In all of these devices, because the motor drive is separate from the sled, and thus needs to be attached, the motor drive is sometimes handled by itself, during which it is possible to drop and damage it. The device presented in U.S. Pat. No. 5,797,858 also allows for a single sterile bag. The required gearing for the longitudinal drive is a part of the sterile disposable catheter assembly, instead of being a part of the pullback device. The pullback device is covered with a single bag and the catheter is snapped in place. There is no bunching of the bag required. Another improvement with this device is that it does not have a separate motor drive and sled that need to be attached to each other. The only attachment step is the attachment of the catheter to the pullback device. However, the additional parts in the catheter increase its cost to manufacture. Thus, there exists a need for a single sterile bag that can enclose both the carriage for the motor drive and the sled of a catheter pullback device and expand as the carriage is translated along the sled.